Production of silver halide photographic emulsions containing a synthetic polypeptide derivative



United States atent Z,7lil,805

Patented June 14, 1955 PRODUCTION OF SILVER HALIDE PHOTO- GRAPHICEMULSIONS CONTAINING A SYNTHETIC POLYPEPTIDE DERIVATIVE Henry WalterWood, Ilford, England, assignor to Ilford Limited, Ilford, England, aBritish company No Drawing. Application September 28, 1953, i Serial No.382,874

Claims priority, application Great Britain October 9, 1952 8 Claims.(Cl. 95-7) graphic emulsions the usual procedure is to causeprecipitation of the required silver halide in an aqueous solution ofgelatin by double decomposition between soluble silver salts and solublehalides, thereafter to set the emulsion obtained, ripen it, shred it andwash it. The washed emulsion is then redispersed in an aqueous medium,optionally with additional gelatin, digested and coated on paper, film,glass or other base to form a lightsensitive photographic material.

In British Patent No. 694,132 a process is described for the productionof gelatino silver halide emulsions which comprises adding to analkaline gelatino silver halide photographic emulsion a proportion of asynthetic polypeptide which is soluble in aqueous alkaline solutions butinsoluble in acid solutions, acidifying the emulsion, separating theprecipitate containing silver halide thus obtained, and redispersing thesaid precipitate in aqueous gelatin. The precipitate may be washed toremove soluble by-products formed in the preparation of silver halidebefore its redispersion in aqueous gelatin, and by suitably selectingthe quantity and gelatin concen tration of the aqueous gelatin used forredispersion, emulsions may be obtained which have a high ratio ofsilver to gelatin. It is explained in the said patent that the chemicalcharacter of the synthetic polypeptide is not critical providing alwaysthat it is soluble in aqueous alkaline solutions and insoluble inaqueous acid solutions. The preferred compounds are polyglutamic acidand the copolymers of glutamic acid with other a-aminoacids.Corresponding compounds in which the glutamic acid is replaced byaspartic acid may also be employed. In all cases the optically active orracernic mirgtures of the compounds may be employed, including mixturesof different synthetic polypeptides.

It has now been discovered that there may be employed, in a process ofthe type just described, derivatives of synthetic polypeptides solublein aqueous solutions at all pH values formed by reacting such asynthetic polypeptide with an aryl sulphonyl chloride or aroyl chlorideor with an aryl isocyanate.

According to the present invention, therefore, a process for theproduction of silver halide photographic emulsions comprises adding toan alkaline silver halide photographic emulsion, of which the colloiddispersion medium is gelatin or polyvinyl alcohol, a proportion of aderivative of a waterand acid-soluble synthetic polypeptide,particularly an aryl sulphonyl, aroyl, or aryl carbamyl derivative,which is soluble in aqueous alkaline solutions but insoluble in acidsolutions, acidifying the emulsions, separating the precipitatecontaining silver halide thus obtained, and redispersing the saidprecipitate in aqueous gelatin or polyvinyl alcohol, and preferably inwhichever of such colloids was present in the original emulsion.

While not confining himself to a particular theory of reaction, theapplicant believes, on the evidence available, that the derivativesattach themselves to the silver halide, which is precipitated onreducing the pH value, leaving the bulk of the gelatin or polyvinylalcohol in solution.

The polypeptides may be produced by the methods generally indicated inBritish Patent No. 694,132, using an appropriate amino acid, such aslysine, which imparts to the polypeptide obtained the desired waterandacidsolubility. It is preferred to employ a polypeptide which is acopolymer of glutamic acid and lysine with or Without other amino acids.The polypeptides are prepared by condensation polymerisation of thecarbonic anhydrides, and the gamma carboxy group of the glutamic acidresidues is protected by esterification, whilst the e-amino group of thelysine is protected by a carbobenzyloxy radicle which is removable bytreatment with phosphonium iodide (or more conveniently by treatmentwith hydriodic acid in glacial acetic acid) after polymerisation hasbeen effected. After removal of carbobenzyloxy groups, the protectivemethyl groups are removed by making the aqueous solution alkaline. Thisalso involves neutralising the hydriodic acid which is present partly incombination with the NHz groups of the polymer and partly as anunavoidable contamination from the reduction. The solution may be madealkaline with, for instance, NaOH or Ba(OH)2. The latter cansubsequently be removed as insoluble B21504 if it is desired to preparethe pure polypeptide. However, NaOH is quite satisfactory since thepresence of sodium ions is not a disadvantage and it is not necessary toisolate the polypeptide. The subsequent reactions proceed readily in theaqueous solution containing sodium iodide and the derivative is readilyisolated by acidification.

The polymerisation may be effected in various solvents, but it ispreferred to employ anhydrous dioxan containing ammonia as catalystsince this process yields polypeptides of high molecular weightespecially suitable for conversion to derivatives suitable for use inthe invention. Nevertheless, solvents such as benzene or pyridine may beemployed. Alternatively, the polymerisation step may be effected byfusing the carbonic anhydrides together.

The following are illustrative procedures for the preparation of apolypeptide suitable for conversion to a polypeptide derivative for usein the present invention.

POLYPEPTIDE A 37 millimols each of e-N-carbobenzyloxy lysine anhye drideand 'y-methyl glutamate anhydride and 10 mM. each of glycine anhydride,leucine anhydride, phenylalanine anhydride and O-acetyl tyrosineanhydride were dissolved in 207 ml. sodium-dried dioxan, and 0.25 mM.ammonia, dissolved in dioxan, added as catalyst. After heating on thewater-bath for 3 days, the viscous mix ture was precipitated with etherand the polymer collected and dried (12.6 g.). The carbobenzyloxyprotective groups were removed from the lysine units by treatment in 150ml. acetic acid under hydrogen with 24 g. phosphonium iodide. Theresulting material was soluble in water and was purified byprecipitating it from the aqueous solution by a mixture of 80 ml.alcohol and 900 ml. diethyl ether. After taking up again in Water,

i the pH of the solution was adjusted to 9, which resulted in the almostinstantaneous removal of the protective ester groups of the glutamicunits and acetyl groups of the tyrosine units. This solution, afterstanding for a day at room temperature, was used directly for thepreparation of derivatives. Its content of polymer was estimated to be9.3 g. The polymer is soluble at all pH values.

3 POLYPEPTIDE B A polypeptide was prepared by the method set forth abovebut using 20 millimols each of e-N-carbobenzyloxy lysine anhydride and'y-methyl glutamate anhydride, and millimols each of glycine anhydride,leucine anhydride, phenylalanine anhydride and O-acetyl tyrosineanhydride.

POLYPEPTIDE C A polypeptide was prepared by the general method indicatedabove but omitting the minor proportions of amino acids so that itcontained only lysine and glutamic acid residues in approximatelyequimolar proportions.

POLYPEPTIDE D 0.21 mol of 'y-methyl glutamate anhydride, 0.21 mol ofe-N-carbobenzyloxy lysine anhydride and 0.28 mol of glycine anhydridewere dissolved in 1.2 litres dry dioxan, with 1.37 mM. ammonia ascatalyst, and heated for 3 days on a boiling water bath. The polypeptidewas isolated by precipitation with ether and dried. Yield 93.5. It wasworked up in batches, e. g. 15.5 g. dry polymer was suspended in 150 ml.glacial acetic acid containing g. anhydrous Hl. The mixture Was warmed,with mechanical stirring, for minutes on a boiling water bath. The redproduct was filtered off and dissolved in ml. water; a small amount ofunreacted material was removed by filtration. The

solution was adjusted to pH 9, stood overnight, and then used directlyfor the preparation of Derivative G (hereinafter referred to). It wasestimated to contain 11.8 g. polypeptide.

POLYPEPTIDE E The steps used in producing Polypeptide A were followedbut using 28 mM. of -methyl glutamic anhydride, 26 mM. ofe-N-carbobenzyloxy lysine anhydride, 39 mM. of glycine anhydride and 18mM. of diamino sebacic di-anhydride. Diamino sebacic di-anhydride, m.pt. C., used in the production of this polypeptide, was prepared by theaction of phosphorus pentachloride on the correspondingdi-carbobenzyloxy compound, 111. pt. 136 C. It is notable for the factthat it is an amino acid which, so far as is known, does not occurnaturally.

Derivatives of the synthetic polypeptides may be obtained by reactingthe side-chain amino groups of the lysine units with an aryl sulphonylchloride or aroyl chloride at a pH in the neighbourhood of 10, or byreacting these groups with an aryl isocyanate at a pH in theneighbourhood of 8. of the tyrosine units may be attacked by thesereagents. The derivative-forming reagents are preferably employed insubstantial excess, e. g. 50-100% excess, over the amount required on atheoretical basis to convert all the lysine amino groups, and it isbelieved that under these conditions all, or substantially all, of suchamino groups are substituted.

The following are illustrative of the procedures used for thepreparation of the polypeptide derivatives.

Derivative A 2.3 g. of Polypeptide A, dissolved in 20 ml. water, wastreated with 0.9 ml. 10% KOH to bring the pH to 10. A solution of 3.3 g.naphthalene-Z-sulphonyl chloride in 5 ml. benzene was added and themixture stirred at 50 C. The pH was maintained at about 10 by additionof 10% KOH, a total of 26 ml. being added. After 20 minutes, the visiblereaction ceased and the mixture was acidified with mineral acid toprecipitate the product. It was purified by repeated dissolution inalkali and precipitation with acid, and was obtained in a yield of 2.2g.

Derivative B 2.6 g. of Polypeptide A in 22 ml. water was mixed Inaddition, the hydroxy groups Cal with 22 ml. of a phosphate buffersoltuion giving pH 8. 1.7 g. phenylisocyanate in 1.7 ml. benzene wasadded and the mixture stirred at 5 C. for 40 minutes and for 30 minutesmore at room temperature. During this time the pH was maintained at 8 bythe addition of 3.5 ml. N NaOH. The insoluble by-product, phenylurea,was filtered oif and the product worked up as for Derivative A. A yieldof 2.8 g. was obtained.

Derivative C Polypeptide B was condensed with naphthalene-2- sulphonylchloride as for Derivative A.

Derivative D Polypeptide B was condensed with B-naphthylisocyanatefollowing the general procedure indicated for preparing Derivative B.

Derivative E Polypeptide C was condensed with naphthalene-2- sulphonylchloride following the general procedure indicated for Derivative A.

Derivative F Polypeptide D was condensed with ,B-naphthoyl chloride. Inthis case, when the aqueous reaction mixture was acidified, some of theby-product, naphthoic acid, was co-precipitated with the product. It wasremoved by extraction with diethyl ether. It may be observed that thiscomplication does not arise where the derivative-forming reagent is anisocyanate or a sulphonyl chloride. When isocyanates are used thebyproducts are insoluble at all pH values and may be filtered off beforethe reaction mixture is acidified. When sulphonyl chlorides are used theby-products are soluble at all pH values and so do not come out ofsolution on acidification.

Derivative G Polypeptide E was condensed with fl-naphthyl isocyanate.

The polypeptide derivatives, although solids, cannot be characterised bymelting points since they are infusible. Their nature may be understoodfrom the following theory.

The parent polypeptides may be represented schematically thus:

i. e. as chains containing the peptide linkages, with sidechainsterminating in cationic groups (from lysine residues) and anionic groups(from glutamic acid residues).

The polypeptide derivatives are prepared by reaction with compoundswhich are known to attack primary amino groups. It is assumed that thefollowing occurs, in alkali:

NHz ArNCO -NH.CO.NH.Ar

isocyanate O O C- O O C- NH ArSOzCl NH.S02 Ar H01 sulphonyl chloride -0O C- O O 0..

-NH: ArC OCl |NH.COAr H01 carboxyl chloride I -O O (3-; O O O- In thisway the basic properties (capacity for combining with protons) of theparent compounds are nullified so that the derivatives are no longerampholytic in nature, but are, in effect, polymeric acids, insoluble atlow PH.

It may be observed that the composition of the initial polypeptides maybe assessed in a semi-quantitative manner by hydrolysis and applicationof partition paper chromatography to the concentrated hydrolysate. Thus,by this method it is possible to detect all six of the amino acids usedin Polypeptide A described above, the strengths of the individual spotsgiving an approximate idea of the relative proportions of these aminoacids in the polypeptide. Paper electrophoresis has also proved veryuseful in checking the qualitative composition of the parentpolypeptides.

The polypeptide derivatives of the present invention present anadvantage over alkali-soluble, acid-insoluble polypeptides themselves,as described in Patent No.

694,132, in that in general a smaller quantity of the polypeptidederivative is required to achieve a similar result.

The invention is illustrated by the following examples which, however,are not to be regarded as limiting it in any way:

EXAMPLE 1 A normal type of gelatino silver iodobrornide photographicemulsion was produced having a gelatin content of 0.25%, a silver halidecontent of 9% w./v. and a pH of about 9. To 1 /2 litres of this emulsionwas added 2.5 g. of Derivative C above dissolved in ml. water at pH 8,the emulsion being just warm. Sulphuric acid (100 ml. 5N.H2SO4) was thenimmediately added to the emulsion to neutralise the alkalinity of theemulsion and provide an excess of acid. (Acetic or hydrochloric acid mayequally well be employed for this purpose.) After a few minutesstanding, the precipitate which formed had collected on the bottom ofthe reaction vessel and the supernatant liquid was then decanted. Theprecipitate was then washed with neutral or weakly acid liquors.

The washed precipitate was then adjusted to pH 8.5-9 by addition ofcaustic alkali and stirred for five minutes at 115 F. It was thenre-dispersed in an aqueous gelatin solution.

EXAMPLE 2 A normal type of gelatino silver iodobrornide photographicemulsion was prepared, having a gelatin content of 1.25% and a silverhalide content of 9% w./v., and a pH of about 9. To 1 /2 litres of thisemulsion was added 5 g. of Derivative G referred to above and theprocedure of Example 1 was then followed, precipitation being effectedby the addition of 100 ml. 5N.H2SO4.

EXAMPLE 2:

A silver bromide in polyvinyl alcohol photographic emulsion was preparedcontaining 3.5% silver bromide, 0.25% polyvinyl alcohol and 0.09 Nammonia. After ripening the emulsion there was added, to 2 litres of theemulsion, 2.5 g. of Derivative H. Precipitation was effected by addingml. 5N.H2SO4 and the precipitate was separated as in the previousexamples and re-dispersed in aqueous polyvinyl alcohol solution.

The precise technique employed will naturally vary with the nature ofthe silver halide emulsion being treated and with the precise characterof the polypeptide derivative. However, in respect of gelatin emulsionsit may be observed in general that the higher the gelatin content of theoriginal emulsion, the greater is the quantity of the polypeptidederivative required. Where the initial emulsion contains sensitisingdyes, these are carried with the silver halide into the precipitate.Where emulsions are prepared according to the present invention and donot contain sensitising dyes, such emulsions may be dyed in the usualway. It is a feature of the present invention that the precipitatecontaining silver halide may be re-dispersed in aqueous gelatin oraqueous polyvinyl alcohol of greater concentration than exists in thesolution from which the precipitate is formed.

What I claim is:

l. A process for the production of silver halide photographic emulsionswhich comprises adding to an alkaline silver halide photographicemulsion of which the colloid dispersion medium is selected from theclass consisting of gelatin and polyvinyl alcohol, a proportion of aderivative of a waterand acid-soluble synthetic polypeptide which issoluble in aqueous alkaline solutions but insoluble in acid solutions,said polypeptide being a copolymer including glutamic acid and lysine,said derivative being selected from the class consisting of arylsulphonyl, aroyl, and aryl carbamyl derivatives of said polypeptide,acidifying the emulsion, separating the precipitate containing silverhalide thus obtained, and redispersing the said precipitate in anaqueous medium containing a colloid selected from the class consistingof gelatin and polyvinyl alcohol.

2. A process for the production of silver halide photographic emulsionswhich comprises adding to an alkaline silver halide photographicemulsion of which the colloid dispersion medium is gelatin, a proportionof a derivative of a waterand acid-soluble synthetic polypeptide whichis soluble in aqueous alkaline solutions but insoluble in acidsolutions, said polypeptide being a copolymer including glutamic acidand lysine, said derivative being a naphthalene sulphonyl derivative ofthe said polypeptide, acidifying the emulsion, separating theprecipitate containing silver halide thus obtained, and redispersing thesaid precipitate in an aqueous medium containing gelatin.

3. A process for the production of silver halide photographic emulsionswhich comprises adding to an alkaline silver halide photographicemulsion of which the colloid dispersion medium is polyvinyl alcohol, aproportion of a derivative of a waterand acid-soluble syntheticpolypeptide which is soluble in aqueous alkaline solutions but insolublein acid solutions, said polypeptide being a copolymer including glutamicacid and lysine, said derivative being a naphthalene sulphonylderivative of the said polypeptide, acidifying the emulsion, separatingthe precipitate containing silver halide thus obtained, and redispersingthe said precipitate in an aqueous medium containing polyvinyl alcohol.

4. A process for the production of silver halide photographic emulsionswhich comprises adding to an alkaline silver halide photographicemulsion of which the colloid dispersion medium is gelatin, a proportionof a derivative of a waterand acid-soluble synthetic polypeptide whichis soluble in aqueous alkaline solutions but insoluble in acidsolutions, said polypeptide being a copolymer including glutamic acidand lysine, said derivative being a naphthyl carbamyl derivative of thesaid polypeptide, acidifying the emulsion, separating the precipitatecontaining silver halide thus obtained, and redispersing the saidprecipitate in an aqueous medium containing gelatin.

5. A process for the production of silver halide photographic emulsionswhich comprises adding to an alkaline silver halide photographicemulsion of which the colloid dispersion medium is polyvinyl alcohol, aproportion of a derivative of a waterand acid-soluble syntheticpolypeptide which is soluble in aqueous alkaline solutions but insolublein acid solutions, said polypeptide being a copolymer including glutamicacid and lysine, said derivative being a naphthyl carbamyl derivative ofthe said polypeptide, acidifying the emulsion, separating theprecipitate containing silver halide thus obtained, and redispersing thesaid precipitate in an aqueous medium containing polyvinyl alcohol.

6. A process for the production of silver halide photographic emulsionswhich comprises adding to an alkaline silver halide photographicemulsion of which the colloid dispersion medium is gelatin, a proportionof a derivative of a waterand acid-soluble synthetic polypeptide whichis soluble in aqueous alkaline solutions but insoluble in acidsolutions, said polypeptide being a copolymer including glutamic acidand lysine, said derivative being a naphthoyl chloride derivative of thesaid polypeptide, acidify ing the emulsion, separating the precipitatecontaining silver halide thus obtained, and redispersing the saidprecipitate in an aqueous medium containing gelatin.

7. A process for the production of silver halide photographic emulsionswhich comprises adding to an alkaline silver halide photographicemulsion of which the colloid dispersion medium is polyvinyl alcohol, aproportion of a derivative of a waterand acid-soluble syntheticpolypeptide which is soluble in aqueous alkaline solutions but insolublein acid solutions, said polypeptide being a copolymer including glutamicacid and lysine, said derivative being a naphthoyl chloride derivativeof the said polypeptide, acidifying the emulsion, separating theprecipitate containing silver halide thus obtained, and redispersing thesaid precipitate in an aqueous medium containing polyvinyl alcohol.

8. A photographic silver halide emulsion of which the dispersion mediumis selected from the class consisting of gelatin and polyvinyl alcohol,containing an alkalisoluble, acid-insoluble derivative of a syntheticpolypeptide which is itself waterand acid-soluble, said polypeptidebeing a copolymer including glutamic acid and lysine and said derivativebeing selected from the class consisting of aryl sulphonyl, aroyl andaryl carbamyl derivatives a said polypeptide.

References Cited in the file of this patent UNITED STATES PATENTSl,7l9,7ll Matthies et a1 July 2, 1929 2,454,001 Mueller Nov. 16, 1948FOREIGN PATENTS 259,926 Great Britain Sept. 26, 1927 500,537 BelgiumJan. 31, 1951

1. A PROCESS FOR THE PRODUCTING OF SILVER HALIDE PHOTOGRAPHIC EMULSIONSWHICH COMPRISES ADDING TO AN ALKALINE SILVER HALIDE PHOTOGRAPHICEMULSION OF WHICH THE COLLOID DISPERSION MEDIUM IS SELECTED FROM THECLASS CONSISTING OF GELATIN AND POLYVINYL ALCOHOL, A PROPORTION OF ADERIVATIVE OF A WATER- AND ACID-SOLUBLE SYNTHETIC POLYEPTIDE WHICH ISSOLUBLE IN AQUEOUS ALKALINE SOLUTIONS BUT INSOLUBLE IN ACID SOLUTIONS,SAID POLYPEPTIDE BEING A COPOLYMER INCLUDING GLUTAMIC ACID AND LYSINE,SAID DERIVATIVE BEING SELECTED FRON THE CLASS CONSISTING OF ARYLSULPHONYL, AROYL, AND ARYL CARBAMYL DERIVATIVES OF SAID POLYPEPTIDE,ACIDIFYING THE EMULSION, SEPARATING THE PRECIPITATE CONTAINING SILVERHALIDE THUS OBTAINED, AND REDISPERSING THE SAID PRECIPITATE IN ANAQUEOUS MEDIUM CONTAINING A COLLOID SELECTED FROM THE CLASS CONSISTINGOF GALATIN AND POLYVINYL ALCOHOL.